The present invention may be used when whole blood is taken from a donor for collection in a sterile fashion in a collecting bag.
To prevent coagulation of the blood in the collecting bag, it is conventional for the collecting bag to be filled prior to extracting with an additive anticoagulant and/or preservation solution.
One of the problems with such a system lies in producing a homogeneous mixture between the solution contained in the bag and the extracted blood. This is conventionally done by stirring the collecting bag.
Another problem posed is controlling the volume proportion of additive solution in the extracted fluid. This is important, in particular in the field of blood collection, because the quantity of anticoagulant and/or preservation solution present in a bag of blood is fixed at a certain proportion so that the blood can be used in the medical field.
To resolve these problems, devices including a bag containing the anticoagulant and/or preservation solution and an initially empty collecting bag have been proposed. In such devices, pumps having two rotors, one for supplying extracted biological fluid and the other for supplying solution, are used. The two rotors rotate at different tangential speeds slaved to one another so as to obtain the required volume proportion of biological fluid and additive solution.
These devices leave ample room for improvement in that they require the use of a special complex pump structure which complicates their use whilst increasing the extraction cost.
In addition, U.S. Pat. No. 4,223,672 discloses an apparatus for the extracorporeal treatment of blood, in which a receptacle containing an anticoagulant is connected to a first tube by way of a fourth tube. This connection is effected upstream of a peristaltic pump which is designed to supply a receptacle with blood by way of the first tube. This patent indicates that the ratio between the cross-sections of the first and fourth tubes is chosen so as to obtain the required mixture of anticoagulant in the blood.
In this type of apparatus, because the connection between anticoagulant and biological fluid is made upstream of the pump, the flow of anticoagulant solution is directed towards the patient. This design therefore has in particular the drawback of risk of injection of anticoagulant solution into the patient.